1. Field of the Invention
The present invention relates to a jet-propulsion personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to an exhaust structure of the personal watercraft capable of preventing water ingress into an exhaust system when the watercraft is inverted, and of producing a high muffling effect.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In general, in the personal watercraft, an exhaust gas from an engine for driving the water jet pump is introduced through an exhaust passage including a water muffler and discharged outside the watercraft through an exhaust outlet provided in a transom board.
The water muffler has an internal structure called xe2x80x9clabyrinth structure,xe2x80x9d capable of preventing water entering through the exhaust outlet from reaching the engine, even when the watercraft is inverted. Such a structure is especially advantageous because waves following behind the watercraft sometimes enter the exhaust outlet when the watercraft is inverted. In particular, in the personal watercraft in which a four-cycle engine is equipped, the water ingress into the engine sometimes affects an engine power characteristic, and, therefore, it is essential that the water ingress into the engine be prevented.
While the water muffler has a muffling function because of its labyrinth structure, a relatively loud exhaust sound is sometimes generated depending on the driving condition of the watercraft, since the exhaust gas is discharged rearwardly through the exhaust outlet located above the planing surface in the above constitution.
In light of environmental problems, such an exhaust sound is needed to be reduced.
As a solution to the above-mentioned problem, U.S. Pat. No. 6,066,014 discloses that a high muffling effect is produced by discharging the exhaust gas into water along a pump cover covering a lower surface of a pump room. However, this constitution is undesirable, because the shape of the pump cover significantly affects a planing performance of the watercraft, and the discharge of the exhaust gas along a planing surface of the pump cover might cause cavitations to occur in the planing surface.
The present invention addresses the above-described condition, and an object of the present invention is to provide an exhaust structure of a jet-propulsion personal watercraft capable of producing a high muffling effect and preventing water ingress into an exhaust system even when the watercraft is inverted.
The above-described object can be achieved by the jet-propulsion personal watercraft constituted as described below.
An exhaust structure of a personal watercraft of the present invention, adapted to eject water pressurized and accelerated by a water jet pump from an outlet port so as to be propelled as the resulting reaction, is adapted to cause an exhaust gas from an engine for driving the water jet pump to be discharged to outside of the watercraft through an exhaust passage. The personal watercraft includes a pump cover covering a pump room, which contains the water jet pump, from the bottom side of the watercraft. The exhaust passage is configured to cause the exhaust gas from the engine to be discharged to outside of the watercraft through a space in a hollow portion partially or entirely formed in the pump cover and a space in the pump room.
In accordance with the above invention, the exhaust gas from the engine is discharged into the pump room through the hollow portion formed by, for example, double-wall structuring of the pump cover, and then is muffled in the pump room. Therefore, a high muffling effect is produced. In addition, since the exhaust gas is discharged from inside of the pump cover to be located at the highest position and above the water surface to outside of the watercraft without being significantly affected by waves following when the watercraft is inverted, the water ingress into the exhaust system can be prevented. In particular, while the watercraft is planing, the pump room can be maintained in a hollow state without water ingress therein, and, therefore, the water ingress into the exhaust system through the hollow portion hardly occurs.
In the above invention, an exhaust outlet of the hollow portion into the pump room is located in a space surrounded by walls of the pump room and the pump cover. This makes it possible that the water ingress into the exhaust system during planing of the watercraft can be effectively prevented. In addition, the hollow portion may be provided to the pump cover or integrally provided with the pump cover, for example by casting.
In the above invention, the exhaust outlet of the hollow portion into the pump room may be opened upwardly or laterally. Therefore, the watercraft can be designed more freely in view of layout of the hull, the water jet pump, the exhaust system, and the like.
In the above invention, the exhaust outlet of the hollow portion into the pump room may be provided at one spot, or otherwise the exhaust gas may be discharged into the pump room through a plurality of branched exhaust passages from the water muffler to the hollow portion.
Furthermore, an exhaust structure of a personal watercraft of the present invention adapted to eject water pressurized and accelerated by a water jet pump from an outlet port so as to be propelled as the resulting reaction, is adapted to discharge an exhaust gas from an engine for driving the water jet pump outside the watercraft through an exhaust passage. The personal watercraft includes a pump room formed by recessing a rear end portion of the hull, for containing the water jet pump, and a pump cover over the pump room and a part of the hull bottom surface extending forward from the pump room from the bottom side of the watercraft. The exhaust passage has a gap, provided between the hull bottom surface and the pump cover, and for communicating the engine with the pump room. The exhaust passage is configured to cause the exhaust gas from the engine to flow into the pump room through the gap and to be discharged outside the watercraft through the pump room.
In the above invention, without the above identified hollow portion, the exhaust gas from the engine is discharged into the pump room through the gap provided between the hull bottom surface and the pump cover, and for communicating the engine with the pump room. The gap allows the exhaust gas from the engine into the pump room therethrough. Therefore, the above mentioned muffling function and water-ingress-proof function can be achieved with a simple constitution.
As a matter of course, in the above invention, the engine may be a two-cycle engine or a four-cycle engine.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.